Compute correct bounds for DrawShadowRec.

Bug: skia:6880
Change-Id: Ia8b94e52eec3feb5104d2351bf7a7e6f99101deb
Reviewed-on: https://skia-review.googlesource.com/26370
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

9 files changed, 163 insertions, 34 deletions

diff --git a/src/core/SkColorSpaceXformCanvas.cpp b/src/core/SkColorSpaceXformCanvas.cpp
index 530552862d..6d6d27b399 100644
--- a/src/core/SkColorSpaceXformCanvas.cpp
+++ b/src/core/SkColorSpaceXformCanvas.cpp
@@ -8,7 +8,7 @@
 #include "SkColorFilter.h"
 #include "SkColorSpaceXformCanvas.h"
 #include "SkColorSpaceXformer.h"
-#include "SkDrawShadowRec.h"
+#include "SkDrawShadowInfo.h"
 #include "SkGradientShader.h"
 #include "SkImageFilter.h"
 #include "SkImagePriv.h"
diff --git a/src/core/SkDrawShadowInfo.cpp b/src/core/SkDrawShadowInfo.cpp
new file mode 100755
index 0000000000..704083b428
--- /dev/null
+++ b/src/core/SkDrawShadowInfo.cpp
@@ -0,0 +1,95 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkDrawShadowInfo.h"
+#include "SkMatrix.h"
+#include "SkPath.h"
+#include "SkRect.h"
+
+namespace SkDrawShadowMetrics {
+
+static SkScalar compute_z(SkScalar x, SkScalar y, const SkPoint3& params) {
+    return x*params.fX + y*params.fY + params.fZ;
+}
+
+void GetLocalBounds(const SkPath& path, const SkDrawShadowRec& rec, const SkMatrix& ctm,
+                    SkRect* bounds) {
+    SkRect ambientBounds = path.getBounds();
+    SkScalar occluderZ;
+    if (SkScalarNearlyZero(rec.fZPlaneParams.fX) && SkScalarNearlyZero(rec.fZPlaneParams.fY)) {
+        occluderZ = rec.fZPlaneParams.fZ;
+    } else {
+        occluderZ = compute_z(ambientBounds.fLeft, ambientBounds.fTop, rec.fZPlaneParams);
+        occluderZ = SkTMax(occluderZ, compute_z(ambientBounds.fRight, ambientBounds.fTop,
+                                                rec.fZPlaneParams));
+        occluderZ = SkTMax(occluderZ, compute_z(ambientBounds.fLeft, ambientBounds.fBottom,
+                                                rec.fZPlaneParams));
+        occluderZ = SkTMax(occluderZ, compute_z(ambientBounds.fRight, ambientBounds.fBottom,
+                                                rec.fZPlaneParams));
+    }
+    SkScalar ambientBlur;
+    SkScalar spotBlur;
+    SkScalar spotScale;
+    SkPoint spotOffset;
+    if (ctm.hasPerspective()) {
+        // transform ambient and spot bounds into device space
+        ctm.mapRect(&ambientBounds);
+
+        // get ambient blur (in device space)
+        ambientBlur = SkDrawShadowMetrics::AmbientBlurRadius(occluderZ);
+
+        // get spot params (in device space)
+        SkPoint devLightPos = SkPoint::Make(rec.fLightPos.fX, rec.fLightPos.fY);
+        ctm.mapPoints(&devLightPos, 1);
+        SkDrawShadowMetrics::GetSpotParams(occluderZ, devLightPos.fX, devLightPos.fY,
+                                           rec.fLightPos.fZ, rec.fLightRadius,
+                                           &spotBlur, &spotScale, &spotOffset);
+    } else {
+        SkScalar devToSrcScale = SkScalarInvert(ctm.getMinScale());
+
+        // get ambient blur (in local space)
+        SkScalar devSpaceAmbientBlur = SkDrawShadowMetrics::AmbientBlurRadius(occluderZ);
+        ambientBlur = devSpaceAmbientBlur*devToSrcScale;
+
+        // get spot params (in local space)
+        SkDrawShadowMetrics::GetSpotParams(occluderZ, rec.fLightPos.fX, rec.fLightPos.fY,
+                                           rec.fLightPos.fZ, rec.fLightRadius,
+                                           &spotBlur, &spotScale, &spotOffset);
+
+        // convert spot blur to local space
+        spotBlur *= devToSrcScale;
+    }
+
+    // in both cases, adjust ambient and spot bounds
+    SkRect spotBounds = ambientBounds;
+    ambientBounds.outset(ambientBlur, ambientBlur);
+    spotBounds.fLeft *= spotScale;
+    spotBounds.fTop *= spotScale;
+    spotBounds.fRight *= spotScale;
+    spotBounds.fBottom *= spotScale;
+    spotBounds.offset(spotOffset.fX, spotOffset.fY);
+    spotBounds.outset(spotBlur, spotBlur);
+
+    // merge bounds
+    *bounds = ambientBounds;
+    bounds->join(spotBounds);
+    // outset a bit to account for floating point error
+    bounds->outset(1, 1);
+
+    // if perspective, transform back to src space
+    if (ctm.hasPerspective()) {
+        // TODO: create tighter mapping from dev rect back to src rect
+        SkMatrix inverse;
+        if (ctm.invert(&inverse)) {
+            inverse.mapRect(bounds);
+        }
+    }
+}
+
+
+}
+
diff --git a/src/core/SkDrawShadowInfo.h b/src/core/SkDrawShadowInfo.h
new file mode 100644
index 0000000000..a08256b8cd
--- /dev/null
+++ b/src/core/SkDrawShadowInfo.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkDrawShadowInfo_DEFINED
+#define SkDrawShadowInfo_DEFINED
+
+#include "SkColor.h"
+#include "SkPoint.h"
+#include "SkPoint3.h"
+
+class SkMatrix;
+class SkPath;
+struct SkRect;
+
+struct SkDrawShadowRec {
+    SkPoint3    fZPlaneParams;
+    SkPoint3    fLightPos;
+    SkScalar    fLightRadius;
+    SkScalar    fAmbientAlpha;
+    SkScalar    fSpotAlpha;
+    SkColor     fColor;
+    uint32_t    fFlags;
+};
+
+namespace SkDrawShadowMetrics {
+
+static constexpr auto kAmbientHeightFactor = 1.0f / 128.0f;
+static constexpr auto kAmbientGeomFactor = 64.0f;
+
+inline SkScalar AmbientBlurRadius(SkScalar height) {
+    return height*kAmbientHeightFactor*kAmbientGeomFactor;
+}
+
+inline SkScalar AmbientRecipAlpha(SkScalar height) {
+    return 1.0f + SkTMax(height*kAmbientHeightFactor, 0.0f);
+}
+
+inline SkScalar SpotBlurRadius(SkScalar occluderZ, SkScalar lightZ, SkScalar lightRadius) {
+    return lightRadius*SkTPin(occluderZ / (lightZ - occluderZ), 0.0f, 0.95f);
+}
+
+inline void GetSpotParams(SkScalar occluderZ, SkScalar lightX, SkScalar lightY, SkScalar lightZ,
+                          SkScalar lightRadius,
+                          SkScalar* blurRadius, SkScalar* scale, SkVector* translate) {
+    SkScalar zRatio = SkTPin(occluderZ / (lightZ - occluderZ), 0.0f, 0.95f);
+    *blurRadius = lightRadius*zRatio;
+    *scale = SkTMax(lightZ / (lightZ - occluderZ), 1.0f);
+    *translate = SkVector::Make(-zRatio * lightX, -zRatio * lightY);
+}
+
+// get bounds prior to the ctm being applied
+void GetLocalBounds(const SkPath&, const SkDrawShadowRec&, const SkMatrix& ctm, SkRect* bounds);
+
+}
+
+#endif
diff --git a/src/core/SkDrawShadowRec.h b/src/core/SkDrawShadowRec.h
deleted file mode 100644
index cc55804891..0000000000
--- a/src/core/SkDrawShadowRec.h
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
- * Copyright 2017 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkDrawShadowRec_DEFINED
-#define SkDrawShadowRec_DEFINED
-
-#include "SkColor.h"
-#include "SkPath.h"
-#include "SkPoint3.h"
-
-struct SkDrawShadowRec {
-    SkPoint3    fZPlaneParams;
-    SkPoint3    fLightPos;
-    SkScalar    fLightRadius;
-    SkScalar    fAmbientAlpha;
-    SkScalar    fSpotAlpha;
-    SkColor     fColor;
-    uint32_t    fFlags;
-};
-
-#endif
diff --git a/src/core/SkLiteDL.cpp b/src/core/SkLiteDL.cpp
index f1101b1be2..1565dae5cc 100644
--- a/src/core/SkLiteDL.cpp
+++ b/src/core/SkLiteDL.cpp
@@ -8,7 +8,7 @@
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkDrawFilter.h"
-#include "SkDrawShadowRec.h"
+#include "SkDrawShadowInfo.h"
 #include "SkImage.h"
 #include "SkImageFilter.h"
 #include "SkLiteDL.h"
diff --git a/src/core/SkPicturePlayback.cpp b/src/core/SkPicturePlayback.cpp
index 1e4fe11b8e..9ebb178aa5 100644
--- a/src/core/SkPicturePlayback.cpp
+++ b/src/core/SkPicturePlayback.cpp
@@ -6,7 +6,7 @@
  */
 
 #include "SkCanvas.h"
-#include "SkDrawShadowRec.h"
+#include "SkDrawShadowInfo.h"
 #include "SkPatchUtils.h"
 #include "SkPictureData.h"
 #include "SkPicturePlayback.h"
diff --git a/src/core/SkPictureRecord.cpp b/src/core/SkPictureRecord.cpp
index 0e1facaa5f..4421633580 100644
--- a/src/core/SkPictureRecord.cpp
+++ b/src/core/SkPictureRecord.cpp
@@ -6,7 +6,7 @@
  */
 
 #include "SkPictureRecord.h"
-#include "SkDrawShadowRec.h"
+#include "SkDrawShadowInfo.h"
 #include "SkImage_Base.h"
 #include "SkPatchUtils.h"
 #include "SkPixelRef.h"
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index 1e69e178c2..df68f8a622 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -457,10 +457,9 @@ private:
     }
 
     Bounds bounds(const DrawShadowRec& op) const {
-        // TODO: compute correct bounds for shadow
-        SkRect shadowBounds = op.path.getBounds();
-        shadowBounds.outset(100, 100);
-        return this->adjustAndMap(shadowBounds, nullptr);
+        SkRect bounds;
+        SkDrawShadowMetrics::GetLocalBounds(op.path, op.rec, fCTM, &bounds);
+        return this->adjustAndMap(bounds, nullptr);
     }
 
     Bounds bounds(const DrawPicture& op) const {
diff --git a/src/core/SkRecords.h b/src/core/SkRecords.h
index 389730404c..8821a3ea2a 100644
--- a/src/core/SkRecords.h
+++ b/src/core/SkRecords.h
@@ -11,7 +11,7 @@
 #include "SkData.h"
 #include "SkCanvas.h"
 #include "SkDrawable.h"
-#include "SkDrawShadowRec.h"
+#include "SkDrawShadowInfo.h"
 #include "SkImage.h"
 #include "SkImageFilter.h"
 #include "SkMatrix.h"